Add error detection self-tests

Adds a new `env` directive EXPECTED_ERRORS, allowing to confirm
if a certain number of errors is in fact detected.
Fix PEP8 and add info message
Detect bad module names to install
Have broken module generate one error
Add failing tests to tested module
Change directive name to SERVER_EXPECTED_ERRORS
Merge pull request #131 from dreispt/test-has-failed

Add self test ability, to check if errors are successfully detected
fix regression in #131

close #148
fix the fix
Merge pull request #149 from gurneyalex/fix-expected-error-regression

fix regression in #131
Merge branch 'master' of github.com:oca/maintainer-quality-tools